(Revised Abstract) DESCRIPTION (provided by applicant): The overall goal of the proposed research is to develop new radiolabeled peptide-peptide nucleic acid (peptide-PNA) constructs for molecular imaging of proto-oncogene expression in cancer. The hypotheses to be addressed in this application are 1) that overexpression of bcI-XL in non-Hodgkin's lymphoma (NHL) can be detected in vivo by radiolabeled antisense PNAs conjugated to peptides for intracellular delivery, and 2) that in vivo imaging of bcI-XL overexpression correlates with poor response to conventional chemotherapy in canine lymphoma patients. The bcI-XL gene is a member of a new category of cellular oncogenes involved in blocking tumor cell apoptosis, which is a major cytotoxic response to chemotherapy and radiotherapy. Furthermore, bcl- XL overexpression is involved in blocking anoikis, or anchorage-dependent apoptosis, and may play a role in tumor invasion and metastasis. The objective of this research application is to synthesize peptide-antisense-PNA conjugates labeled with the diagnostic imaging radiometal 111In and evaluate these radiopharmaceuticals for bcl- XL mRNA targeting in vitro and in vivo. These goals will be accomplished by synthesizing new bcI-XL antisense PNAs conjugated to peptides for intracellular delivery (Specific Aim 1), evaluating the bcI-XL mRNA binding properties of the peptide-PNA conjugates by Northern blot analysis (Specific Aim 2), performing in vitro cell uptake, internalization, efflux, and fluorescence microscopy studies of the peptide-PNA conjugates in bcI-XL -positive and -negative lymphoma cell lines in culture (Specific Aim 3), performing biodistribution and microSPECT imaging studies in SCID mice bearing human NHL xenografts, in order to select the optimal tumor targeting conjugate (Specific Aim 4), and evaluating the optimal 111In- labeled anti-bcI-XL peptide-PNA construct by performing gamma scintigraphy studies in canine lymphoma patients receiving conventional chemotherapy, in order to determine whether in vivo bcI-XL imaging correlates with treatment outcome (Specific Aim 5).